The present invention relates to a magnetic brush developing apparatus for use in electrographic copying machines and the like, and more particularly to a magnetic brush developing apparatus for developing latent electrostatic images with a magnetic developer.
Conventional methods of developing latent electrostatic images are divided into two general categories: dry and wet. Dry developing methods are further divided into two types: those in which two-component developers are used, and those in which mono-component developers are used. Magnetic developers, whether of the two-component type or of the mono-component type, have been predominantly used in recent developing methods.
For use in developing methods which employ such magnetic developers, magnetic brush developing apparatus are known which include a nonmagnetic developing sleeve having a magnetic roller incorporated therein. In such apparatus, the developer is transported on the sleeve by rotating the sleeve or the internal magnetic roller, or by rotating both the sleeve and the roller at the same time.
With magnetic brush developing apparatus of the type mentioned, the thickness of the developer layer on the sleeve, namely the bristle height of the magnetic brush, is adjusted usually by the use of a restricting plate 4 or restricting roller 5 as shown in FIG. 1 or 2. Indicated at 1 in FIGS. 1 and 2 is a developing sleeve, at 2 a magnetic roller rotatably housed in the sleeve 1, and at 3 a developer hopper. By the rotation of the sleeve 1 and/or the magnetic roller 2, a developer 13 is transported on the sleeve 1 counterclockwise to a developing position C and made into a layer of specified thickness by the restricting plate 4 or restricting roller 5 in the course of transport.
However, the magnetic brush developing apparatus in which the bristle height is restricted by this method has the following problems.
(1) Developer particles are likely to agglomerate or cake between the restricting member and the sleeve, thus failing to form a uniform developer layer.
(2) Especially when the apparatus is adapted to transport the developer by the rotation of the magnetic roller, the force of transport, which is created by the revolution of the developer, is small and is therefore greatly influenced by the force of the restricting member acting against the transport, so that the developer is likely to form an uneven layer as stated in paragraph (1). Consequently, such developing apparatus has difficulties in effecting satisfactory development.
(3) The restricting plate, roller or like rigid body must be held at a specified distance from the sleeve and made delicately adjustable for the restriction of the bristle height, using a mechanically complex arrangement.